A word that’s used a lot when talking about sound reproduction is “imaging.” But what, exactly, does imaging mean in audio? And how does imaging relate to a sound-field or soundscape? How do we perceive imaging? How important is imaging to our enjoyment?
In sound, imaging is the ability to close your eyes and still perceive the locations of sources of sonic events. The terms sound-field and soundscape are used interchangeably. A sound-field or soundscape exists when multiple sonic events are taking place at the same time and the sources are independently located in space. The soundscape is sharp, focused or detailed when the different sources are clearly separate. The sound-field is fixed or stable if the individual sources stay in the same individual locations as you listen.
There has been much research on how we locate sound sources. Our two ears and brain make a very powerful, real-time audio analyzer. The technique our ear/brain audio processor uses to determine locations of sound sources varies with frequency. In the treble (about 2000 Hz and above) our head produces shadowing. This shadow produces different sound balances from one ear to the other when the source is not directly in front or behind us. Our brain uses the differences to locate the source. (An interesting note: front-center and rear-center locations are often confused since they have no shadow.) In the mid-bass (about 80-800 Hz) the time delay between when the sound reaches each ear is the major technique for locating the source. Through the midrange (about 500-3000 Hz) both processes are used. Most voices fall in or near these midrange frequencies. This makes voices among the easiest sounds to locate and have the sharpest discriminations.
Since the invention of music recording and playback, the goal has been to be convinced that you are in the room with performers. Often it requires closing your eyes as we have been trained to confirm with our eyes what our ears hear. With a single performer, mono worked. Then stereo added width. Now, multi-channel systems are improving height, depth, and full surround effects.
In terms of live performance, different venues have different acoustic personalities or soundscapes. That is, one concert hall can sound different from another – even if they share the same dimensions – and both will sound different from a cabaret space or an arena. Nearly 30 years ago, Yamaha pioneered the technique of capturing the acoustic personality of a space, encoding it in IC chips so that a multi-channel audio system could deliver the “experience of being there” more accurately. They called the process, “Digital Sound-Field Processing.”
Even with the newest electronic technology, creating these sound-fields or soundscapes is a tough test for most speakers. Being able to do it for several listening positions at the same time is even tougher.
Multi-channel or two-channel, hearing the location of sound sources within a space is both one of the challenges of home audio and one of its greatest pleasures. At Ohm, we aim to design speakers that meet the challenge and deliver the pleasure. The current Ohm Walsh speakers provide the cues our ears need to have a wide Sweet-Sweep where the soundscape stays focused and stable for several listening locations.
Ultimately, the listener is the judge.
Enjoy & Good Listening!
John Strohbeen Author
John Strohbeen is the president of Ohm Speakers.